#include<stdio.h>

int sum(int x)
{
	int re = 0;
	for(int i = 1;i <= x;i++)
	{
		re += i;
	}
	return re;
}
double fun(int n)
{
	double re = 0;
	for(int i = 1;i <= n;i++)
	{
		re += 1/(double)sum(i);
	}
	return re;
}
int main()
{
	int num = 0;
	scanf("%d",&num);
	printf("%lf",fun(num));
	
	return 0;
}
